HomeMy WebLinkAboutTIMBERLINE FARMS PUD, DIAMOND SHAMROCK CORNERSTORE - PRELIMINARY - 42-89C - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTn
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Preliminary Drainage Report
Timberline Farms Cornerstore, P.U.D.
Diamond Shamrock
Timberline Road & Milestone Drive
City of Fort Collins, Colorado
June 1994
Prepared for:
Diamond Shamrock Inc.
529 E. 56th Avenue
Denver, CO 80216
(303) 297-9777
Attn: Scot Williamson
Prepared by:
Galloway, Romero & Associates
14202 E. Evans Avenue
(303) 745-7448
Attn: David L. Jones
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Table of Contents
Page
Introduction 1
General Location and Description 1
Drainage Criteria 1
Historic Drainage 2
Developed Drainage 2
Drainage Conclusion 3
Erosion Control 4
Appendix
Vicinity Map A.1
Fig. 3-1 Rainfall Intensity Duration Curve A.2
Estimate of Average Flow Velocity A.3
Composite Runoff Coefficients A.4
Runoff Calculations
10 Year Historic A.5
100 Year Historic A.6
10 Year Developed A•7
100 Year Developed A•$
Historic Drainage Map Back Pocket
Developed Drainage Plan of this report
• Introduction
This report is being prepared for Diamond Shamrock Inc., the
future owner of the site, to fulfill the preliminary drainage
requirements of the City of Fort Collins, Colorado. The report
analyzes onsite and offsite runoff from the initial (10 year
frequency) and major (100 year frequency) storms and routes these
flows through the site. Most of the runoff exits on the northeast
corner via the curb cut on Milestone Drive. Milestone Drive flows
to the northeast to Sunstone Village 8th Filing. Runoff eventually
is detained by Basin 1 detention pond as identified in the Master
Drainage Report for Timberline Farm P.U.D., July 1989. This pond
flows by pipe and swale to detention pond 2, then to the Harmony
Village Mobile Home Park detention pond and finally to the Sunstone
regional detention pond in accordance with the Fox Meadows Basin
Drainage Master Plan.
General Location and Description
The 1.035 acre site is located in the SW 1/4 of Section 32,
Township 7 North, Range 68 West, of the Sixth Principle Meridian,
• City of Fort Collins, Larimer County, Colorado. It is bound by
Timberline Road on the west and by Milestone Drive (future) on the
north. The south and east property is undeveloped and zoned EP.
Currently the site is undeveloped and covered with native
grasses and weeds. The site slopes downward to the northeast
corner of the property. Approximately 0.844 acres south of the
property contributes offsite flow to the site.
The site does not lie within a designated flood hazard area
according to the Flood Insurance Rate Map Community Panel No.
080102-0006.
Drainage Criteria
This report was prepared using criteria as outlined in the
City of Fort Collins "Storm Drainage Design Criteria and
Construction Standards". Runoff for the initial storm, 10 year
frequency, and the major storm, 100 year frequency, was calculated
using the rational method. Times of concentration were calculated
• using the overland flow equation and estimates of average flow
velocity. Composite runoff coefficients were calculated for the
individual basins. On -site detention is not a requirement as
outlined in the Master Drainage Report for Timberline Farm P.U.D.
Runoff calculations with applicable charts and graphs are included
in the Appendix of this report.
Historic Drainage
The undeveloped site is divided up into two basins A and B.
Each onsite basin has an offsite basin, 1 and 2 respectively, that
contributes runoff on to the site.
Offsite Basin 2 is a 0.516 acre basin, bordered by Timberline
Road on the west and the site's south property line on the north.
This area is currently undeveloped and flows unconcentrated on to
site Basin A. Basin A is a 0.816 acre basin along the western
portion of the site. The runoff exits along the north property
line at rates of 0.90 cfs and 1.52 cfs for the 10 and 100 year
storm occurrence, respectively.
• Offsite Basin 2 is a 0.328 acre basin bordered by offsite
Basin 1 on the west and the site's south property line on the
north. This area is currently undeveloped and flows unconcentrated
on to site Basin B. Basin B is a 0.219 acre basin along the
eastern portion of the site. The runoff exits along the east
property line on to the adjacent property to the east at rates of
0.35 cfs and 0.60 cfs for the 10 and 100 year storm occurrences,
respectively.
Developed Drainage
The site is divided into four developed drainage basins, A,
B, C and D. Basin A is a 0.163 acre basin, along the north and
west property lines. This area consists of landscaping. The 10
and 100 year runoff of 0.18 and 0.30 cfs, respectively, exits along
the street gutters of Milestone Drive and Timberline Road. These
flows then travel north along Timberline Road.
Basin B is a 0.436 acre basin consisting of the north and west
paved areas including most of the canopy and convenience store.
2
The 10 and 100 year runoff of 1.92 and 3.18 cfs, respectively,
exits the site via the curb cut on Milestone Drive. The runoff
then flows east along Milestone Drive.
Basin C is a 0.386 acre basin consisting of the remainder of
the paving, the car wash, and landscaping. The 10 and 100 year
runoff of 1.26 and 2.09 cfs, respectively, drains to the southeast
corner of the site then through a channel to the common drive area
near the curb cut on Milestone Drive. The runoff then flows east
along Milestone Drive.
Basin D is a 0.012 acre basin in the southwest corner of the
site. The 10 and 100 year runoff of 0.05 and 0.08 cfs,
respectively, flows to the gutter along Timberline Road. The
runoff then flows north along Timberline Road.
Drainage Conclusion
This report has been prepared using the criteria outlined in
the City of Fort Collins "Storm Drainage Design Criteria and
• Construction Standards". Runoff from the initial and major storms
has been calculated and routed through the site. Regional
detention ponds should be examined as the entire Timberline Farm,
P.U.D. area is developed to confirm adequate capacity.
•
Historic flows must be temporarily diverted until the
remainder of Timberline Farm P.U.D. is developed. Milestone Drive
will be constructed approximately two feet higher than the existing
ground. The proposed development must meet the road elevation
thus, the south property line of the development was raised
approximately one foot to maintain drainage. This will create a
dam effect along the south property line for the offsite basins
flowing north. These offsite flows will have to be diverted to the
northeast around the developed site until adjacent development
occurs. When the adjacent property is developed, runoff will be
able to flow along the common access drive along the east property
line.
3
0 Erosion Control
The site soil is comprised of a slightly sandy clay for the
first ten feet in depth. The soil conditions do not present a
hazard to the proposed development. The site is located within the
moderate wind erodibility zone according to the "Wind Erodibility
Map" contained within the "Storm Drainage Design Criteria and
Construction Standards."
During construction, water erosion should be minimized by
placing hay bales along the north and a portion of the east and
west property lines. The fill imported to raise the site
approximately one foot should divert offsite water away from the
site, further decreasing the potential for water erosion caused by
offsite flows.
The construction period is projected to be late summer and
early fall, for approximately three months. Wind erosion may not
be a significant concern. If the end of the project continues
beyond November 1, then wind erosion may develop. However, most of
the site should be paved and buildings constructed prior to then.
iThis leaves approximately 27 percent of the site with landscaping.
This reduction in area subject to wind erosion should lessen the
erosion considerably and if the landscaping is not fully in place
by November 1, then wind barriers can be installed to further
reduce erosion.
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APPENDIX
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0 VICINITY MAP
SCALE: 1" =2000'
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ESTIMATE OF AVERAGE FLOW VELOCITY FOR
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*MOST FAECUENTLY OCCURRING "UNDEVELOPED"
LAND SURFACES IN THE DENVER REGION.
REFEftE3iCZ: "Urban Hydrology For Small Watersneds" Teennieal
Release No. 55, 11S13A. SCS Jan. 1975.
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Timberline Farms Comerstore, P.U.D.
Diamond Shamrock, Inc.
Timberline Road & Milestone Drive
Composite Runoff Coefficients for Developed Drainage Basins
Basin
Overall
Area
(SF)
Landscaped
Area
(SF)
Landscape
Coefficient
Paved
Area
(SF)
Paved
Coefficient
Roof
Area
(SF)
Roof
Coefficient
Composite
Coefficient
A
7116
7116
0.25
0
0.95
0
0.95
0.25
B
20649
856
0.20
15729
0.95
4064
0.95
0.92
C
16812
4740
0.20
10078
0.95
1994
0.95
0.74
D
516
0
0.20
516
0.95
0
0.95
0.95
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